Section 4 Section 4 GEOLOGY AND SOILS SOURCES OF DATA........................................................................................................................... 4-1 HISTORICAL CONTEXT .................................................................................................................... 4-1 AREA OVERVIEW .............................................................................................................................. 4-2 MAJOR LANDFORMS......................................................................................................................... 4-2 GEOLOGY........................................................................................................................................... 4-2 Significant Geologic Units of the Coast Range Province ......................................... 4-3 Significant Geologic Units of the Great Valley Province......................................... 4-3 SOIL TYPES........................................................................................................................................ 4-6 Columbia-Vina.................................................................................................................... 4-6 Maywood-Tehama.............................................................................................................. 4-6 Corning-Redding ................................................................................................................ 4-7 Newville-Dibble.................................................................................................................. 4-8 Millsholm-Lodo ................................................................................................................... 4-8 Toomes-Guenoc ................................................................................................................. 4-8 Maymen-Los Gatos-Parrish.............................................................................................. 4-9 Henneke-Stonyford ........................................................................................................... 4-9 SOIL CAPABILITIES......................................................................................................................... 4-10 EROSION POTENTIAL..................................................................................................................... 4-12 DATA GAPS...................................................................................................................................... 4-13 CONCLUSIONS AND RECOMMENDATIONS.................................................................................. 4-13 REFERENCES ................................................................................................................................... 4-13 TABLES 4-1 Percent Soil Type....................................................................................................................... 4-10 4-2 Soil Capability Classifications by Soil Association................................................................ 4-12 FIGURES 4-1 Geologic Provinces 4-2 Geology 4-3 Faults 4-4 STATSGO Soil Types 4-5 Soil Hazard Erosion Ratings Section 4 GEOLOGY AND SOILS Basic information on the geology and soils of the Tehama West Watershed is presented in this section. The geology portion includes an area overview and discussion of prominent geologic units and associated faults. The soils portion includes a discussion of primary soil types, soil capabilities, erosion potential, channel migration, and change. Data gaps, conclusions, and recommendations are included at the end of the section. SOURCES OF DATA Primary sources of data used to create this section of the watershed assessment include: x 1962 Geologic Map of California, Redding Sheet. U. S. Geologic Survey (USGS), California Division of Mines and Geology x 1960 Geologic Map of California, Ukiah Sheet. USGS, California Division of Mines and Geology x California Department of Water Resources (DWR). 1982 Thomes Creek Watershed Study x DWR. 1992 Sacramento Valley Westside Tributary Watersheds Erosion Study x U.S. Department of Agriculture. State Soil Geographic Database (STATSGO) (USDA 2005). Additional references are included at the end of the section. HISTORICAL CONTEXT Although geology and soils have not changed appreciably in recent times, land use practices have exerted tremendous influence over hillslope and fluvial processes in watersheds since the arrival of Europeans nearly 150 years ago. Impacts from various mining, logging, farming and ranching, and industrial activities created significant sediment loading to the Sacramento River and its tributary streams. During the late 1800s and early 1900s cattle ranching, sheep herding, and timber harvesting activities developed into major industries in the region and throughout much of the West. These activities influenced native vegetation and production of surface soils. In some areas these changes increased runoff and delivery of sediment to streams via logging roads and crossings, land conversion, landsliding, and direct stream alterations. Tehama West Watershed Assessment Geology, Geomorphology, and Soils 70453 Page 4-1 AREA OVERVIEW The Tehama West Watershed encompasses an area of approximately 1,050 square miles, which includes a diverse landscape of geologic features critical to Tehama County’s agricultural and mining industries. Mountain ranges along the western border of the assessment area reach elevations of approximately 7,500 feet (Solomon Peak) and are comprised of steep slopes and rock types susceptible to erosion. Two primary drainages, Elder Creek and Thomes Creek, continuously transport and deposit the eroded sediments along flood plains of the Sacramento River. It is has been noted that, in general, streams originating from the Coast Ranges produce the highest sediment yields of all the Sacramento River tributaries. An analysis by the USGS showed that the annual suspended sediment yield of Thomes Creek is nearly three times higher than other streams of comparable size (DWR 1982, Jones et al 2000). Many other drainages also exist throughout the watershed and play a vital role in the development of the Sacramento Valley. MAJOR LANDFORMS Many landforms are visible throughout the assessment area, the majority of which include mountains, foothills, and flood plains. Depositional features such as alluvial fans and terrace deposits are also common. Fluvial erosion, hillslope erosion, and mass wasting are attributed to the development of each of these landforms. A flood plain is an area subject to periodic flooding that is hydrologically connected to a stream and consists of unconsolidated materials from streams. Flood plains are typically the most productive areas for natural vegetation and agriculture, and are intrinsically important to the function of natural river systems (USDA SCS 1967, Ritter et al. 1995, Keppen and Slater 1996). Alluvial fan and terrace deposits that form the foothills are located in the central portion of the assessment area. Alluvial fans often develop when sediment is deposited at the transition of a narrow canyon and a valley floor, generating an open fan appearance when viewed from above. Erosional activities, including sheetwash, rill erosion, soil creep, and channel erosion, create dissected terraces. Mass wasting processes, such as rock falls, debris flows, and landslides, dominate landform evolution in the mountainous areas of this region and are initiated by freeze-thaw processes and infrequent precipitation events. These processes create characteristically steep, rocky cliffs and bedrock-controlled stream channels. GEOLOGY California is divided into 11 geologic provinces, each characterized by unique, defining features based on geology, topographic relief, and climate. The Tehama West Watershed includes portions of the eastern Coast Range and western Great Valley Geologic Provinces. The Coast Range Province is characterized by north northwest-trending mountain ranges composed of thick Mesozoic and Cenozoic (240 million years old) strata generally rising 2,000 to 4,000 feet. The Coast Range Province is commonly characterized by zones of extensive shearing and the presence of ophiolite/serpentinite melanges (Jayko 1987). The western portion of the province is Tehama West Watershed Assessment Geology, Geomorphology, and Soils 70453 Page 4-2 distinguished by ridges and valleys of upper Mesozoic sedimentary rocks overlain by alluvium of the Great Valley Province. Included within the Coast Range Province are highly erosive rocks of the Franciscan Complex, which produce large amounts of both suspended sediment and gravel (Blake et al. 1999, CH2M Hill 2002). The headwaters of Red Bank Creek, Elder Creek, and Thomes Creek are located in the Coast Range Province. The Great Valley Province is a sedimentary basin approximately 400 miles long by 50 miles wide, located throughout the central portion of California. In the watershed, the province is characterized by a thick deposit of moderately deformed Jurassic and Cretaceous marine sedimentary layers that consist of detrital materials derived from uplifted basement rocks of the Klamath Mountain and Coast Range Provinces. Great Valley rocks consist primarily of mudstone, shale, and sandstone and occur mostly along the west side of the central valley. These units yield an abundance of suspended sediment but relatively little gravel to drainages. A map showing the geologic provinces is